Whilst on it's own, the value of social bookmarking is questionable/debatable, there is aplace for social bookmarking and great leverage from utilising these to gain additional traffic. This unfortunately doesn't happen overnight and quite often consists of building a decent following on social media overtime to get your social bookmarking submissions shared.
As with any marketing strategy however, the key is to 'mix it up' and there's certainly no harm in mixing a few backlinks from worthwhile social bookmarking sites into your link profile. Knowing which to target, spend any time on and which will be around in a year from now (social bookmarking websites come and go frequently) comes with experience though.
There are of course those businesses that still think social bookmarking is a powerful online strategy in itself and will request 2000 submissions ignoring any advice we have on the matter - this too, if requested, is something we could initiate for you as well.